KR102195952B1 - Powder magnetic core manufacturing method, and powder magnetic core - Google Patents

Abstract

In the manufacturing method by simple pressure molding, there is provided a method for manufacturing a powdered magnetic core capable of responding to complex shapes while securing high strength and insulation. The present invention is a method of manufacturing a powdered magnetic core using a metallic soft magnetic material powder, comprising a first step of mixing the soft magnetic material powder and a binder, and then spray drying, and a second step of press-molding the mixture obtained through the first step. And a third step of performing at least one of grinding and cutting on the formed body obtained through the second step, and a fourth step of heat treating the formed body through the third step, wherein in the fourth step It is characterized in that by heat-treating the molded body, an oxide layer containing an element contained in the soft magnetic material powder is formed on the surface of the soft magnetic material powder.

Description

Powder magnetic core manufacturing method, and powder magnetic core

The present invention relates to a powdered magnetic core and a method of manufacturing a powdered magnetic core constructed using soft magnetic material powder.

Conventionally, coil components such as inductors, transformers, and chokes have been used for a wide variety of applications such as home appliances, industrial devices, and vehicles. The coil component is composed of a magnetic core and a coil wound around the magnetic core. As such a magnetic core, ferrite, which is excellent in magnetic properties, shape freedom, and price, is widely used.

In recent years, as a result of miniaturization of power supplies such as electronic devices, the demand for a coil component that is small and low-powered, and can be used even for high currents is strong, and the magnetic core has a higher saturation magnetic flux density than ferrite. Adoption of a powdered magnetic core using a metallic magnetic powder is in progress. As the metallic magnetic powder, for example, Fe-Si-based, Fe-Ni-based, Fe-Si-Al-based, and the like are used.

Further, a powdered magnetic core obtained by consolidating a metallic magnetic powder such as Fe-Si has a high saturation magnetic flux density, whereas since it is a metallic magnetic powder, its electrical resistivity is low. Therefore, a method of improving the insulation between magnetic powders, such as molding after forming an insulating coating on the surface of the magnetic powder, has been applied. In addition, Patent Document 1 discloses an example in which Fe-Cr-Al-based magnetic powder is used as a magnetic powder capable of generating magnetism of a material with high electrical resistance to be an insulating coating. In Patent Document 1, by oxidizing the magnetic powder, an oxide film having high electrical resistance is formed on the surface of the magnetic powder, and the magnetic powder is solidified by electric discharge plasma sintering to obtain a green magnetic core.

In addition, in Patent Document 2, an oxide layer formed by oxidizing the particles on the surface of the soft magnetic alloy particles containing iron, chromium and silicon is generated, and the oxide layer contains more chromium than the alloy particles, and the particles are A configuration in which the oxide layer is interposed is disclosed.

Patent Document 1: Japanese Laid-Open Patent Publication No. 2005-220438 Patent Document 2: Japanese Laid-Open Patent No. 2011-249836

In the case of using a structure in which a coil is wound around a small compact magnetic core obtained by pressure molding as the coil component, the strength of the compact magnetic core is insufficient, and thus the compact magnetic core is liable to be damaged when the coil is wound. In order to increase the strength of the metal powder core, a large molding pressure is required, and therefore, there have also been problems in manufacturing equipment such as an enlarged apparatus for generating a high pressure, or a mold for molding is liable to be damaged by applying a high pressure. For this reason, there is a limit to the strength of the powdered magnetic core obtained in practical use. In addition, in the case of molding after forming the insulating coating on the surface of the alloy powder as described above, the shape freedom of the obtained molded body is relatively high, but when the molding pressure is increased to increase the strength of the molded body, the insulating coating between the magnetic powders is damaged and the insulation is lowered. There was also a problem.

On the other hand, the configuration described in Patent Document 1 does not require the high pressure as described above, but is a manufacturing method that requires complicated equipment and a lot of time. Further, since a step for pulverizing the agglomerated powder after oxidation treatment of the magnetic powder is required, there is a problem that the step becomes complicated. In addition, although the method disclosed in Patent Document 1 is advantageous in improving insulation and strength, it has been difficult to manufacture a magnetic core having a complex shape such as a drum shape.

The configuration disclosed in Patent Document 2 forms an insulating layer by heat treatment in an oxidizing atmosphere, so that the formation of the insulating layer becomes easy, but does not provide a suitable manufacturing method for a magnetic core having a complex shape.

Accordingly, in view of the above problems, an object of the present invention is to provide a method of manufacturing a powdered magnetic core capable of responding to a complex shape while securing high strength and insulation in a method of manufacturing a powdered magnetic core by simple pressure molding. Further, an object of the present invention is to provide a metal powder core having high strength and insulation in a typical drum-shaped powder metal core as a complex shape.

The method of manufacturing a powdered magnetic core of the present invention is a method of manufacturing a powdered magnetic core using a metallic soft magnetic material powder, wherein a first step of mixing a soft magnetic material powder and a binder, and a mixture obtained through the first step are press-molded. A second step, a third step of performing at least one of grinding and cutting on the formed body obtained through the second step, and a fourth step of heat treating the formed body through the third step, and the fourth step In the above, by heat treatment of the molded body, an oxide layer containing an element contained in the soft magnetic material powder is formed on the surface of the soft magnetic material powder.

Further, in the method for manufacturing a powdered magnetic core, it is preferable that the first step includes a step of spray drying a slurry containing the soft magnetic material powder and a binder.

Further, it is preferable that the soft magnetic material powder is an Fe-Cr-Al-based soft magnetic material powder.

Further, in the manufacturing method of the powdered magnetic core, it is preferable to have a preheating step of heating the molded body to a temperature lower than the heat treatment temperature in the fourth step between the second step and the third step.

Further, in the manufacturing method of the powdered magnetic core, it is preferable that the area ratio of the molded article provided in the third step is 78 to 90%. Further, in the third step, it is preferable that the processing to be performed on the molded article obtained through the second step is cutting.

Further, in the manufacturing method of the powdered magnetic core, it is preferable that at least one of the grinding and cutting is performed on at least a wire winding portion of the powdered magnetic core. Further, in the manufacturing method of the powdered magnetic core, it is preferable that the shape of the powdered magnetic core is a drum shape having flange portions on both ends of the wire winding portion.

The dusting magnetic core of the present invention is a dusting magnetic core composed of metal-based soft magnetic material powder, and has a drum shape having a lead winding portion and flange portions at both ends of the conductor winding portion, and the arithmetic average roughness of the surface of the conductor winding portion is It is larger than the arithmetic average roughness of the outer surface of the flange portion, the metallic soft magnetic material powder is bonded through an oxide layer containing an element contained in the soft magnetic material powder, and the surface of the wire winding portion is a processed surface, In addition, it is characterized in that it has an oxide layer containing an element contained in the soft magnetic material powder.

Further, in the powdered magnetic core, in the drum shape, it is preferable that at least one maximum dimension of both end-side flange portions is larger than the dimension in the axial direction.

Further, in the powdered magnetic core, it is preferable that the soft magnetic material powder is an Fe-Cr-Al-based soft magnetic material powder.

Advantageous Effects of Invention According to the present invention, in a method of manufacturing a powdered magnetic core using simple pressure molding, it is possible to provide a manufacturing method capable of responding to complex shapes while ensuring high strength and insulation.

Further, according to the present invention, it is possible to provide a metal powder core having high strength and insulation in a drum-shaped powder powder core having a typical complex shape.

1 is a process flow chart for explaining an embodiment of a method for manufacturing a powdered magnetic core according to the present invention.
2 is a process flow chart for explaining another embodiment of a method for manufacturing a powdered magnetic core according to the present invention.
3 is an SEM photograph of a cross-section of a metal powder core.
4 is an SEM photograph of a cross-section of a metal powder core.
5 is an SEM photograph of a cross-section of a metal powder core.
6 is an SEM photograph of a cross-section of a metal powder core.
Fig. 7 is a perspective view showing the shapes of a molded body before processing and a molded body after processing (dusting magnetic core).
8 is a perspective view showing an electrode arrangement for measuring the resistance of a green magnetic core.
9 is a process flow chart for explaining another embodiment of a method for manufacturing a powdered magnetic core according to the present invention.
10 is a graph showing the relationship between the preheat treatment temperature and the strength of the green magnetic core.

Hereinafter, an embodiment of a powdered magnetic core and a method of manufacturing a powdered magnetic core according to the present invention will be described in detail, but the present invention is not limited thereto.

1 is a process flow diagram for explaining an embodiment of a method for manufacturing a metal powder core according to the present invention. The manufacturing method shown in FIG. 1 is a method of manufacturing a green magnetic core using a metallic soft magnetic material powder, wherein a first step of spray drying after mixing a soft magnetic material powder and a binder, and a mixture obtained through the first step A second step of press-molding, a third step of performing at least one of grinding and cutting (hereinafter referred to as “grinding, etc.”) on the molded article obtained through the second step, and the third step It has a 4th process of heat-processing a rough green body. By heat-treating the molded body in a fourth step, an oxide layer containing an element contained in the soft magnetic material powder is formed on the surface of the soft magnetic material powder.

By forming such an oxide layer in the heat treatment in the fourth step, bonding and insulation between soft magnetic material powders are realized, and a powdered magnetic core having high strength and high insulation properties is obtained. Since the formation of an insulating oxide layer on the surface of the soft magnetic material powder is possible only by performing heat treatment on the molded body, the step of forming the insulating coating is also simplified. In addition, one of the features of the present invention is that prior to the fourth step in which high strength is imparted to the powdered magnetic core, a third step is performed to obtain a predetermined shape, dimensions, and the like.

The high-strength powdered magnetic core is provided by the oxide layer formed by the heat treatment in the fourth step, but on the contrary, since it is high-strength, processing after the heat treatment becomes difficult. In addition, when processing is performed after the heat treatment, since the metal portion of the soft magnetic material powder is exposed to the portion, insulation properties cannot be ensured as it is. Therefore, a flow of forming an oxide layer by performing a heat treatment after finishing a grinding process or the like for forming a predetermined shape before the fourth step is adopted. The radial crushing strength of the molded body immediately after passing through the second step is, for example, about 5 to 15 MPa, and is about 1/10 or less of the crushing strength of the magnetic core subjected to the heat treatment in the fourth step. Therefore, in the state of the molded body immediately after passing through the second step, grinding processing or the like is easy. Further, even if the metal part is exposed by grinding or the like, the part is covered with the oxide layer by undergoing heat treatment in the fourth step. Therefore, by employing the above flow, the problem of workability and the problem of insulation are solved all at once.

First, the soft magnetic material powder provided in the first step will be described. The metallic soft magnetic material powder is not particularly limited as long as it has magnetic properties capable of constituting a green magnetic core, and can form an oxide layer containing an element containing the soft magnetic material powder on the surface of the soft magnetic material powder. , Various ferromagnetic raw metals and ferromagnetic alloys can be used. A preferred form of the metallic soft magnetic material powder is, for example, Fe-Cr-M (M is at least one of Al and Si). Since the Fe-Cr-M-based alloy powder contains Cr in addition to Fe as the base element, it is superior in corrosion resistance, for example, compared to the Fe-Si-based alloy powder. In addition, since Al and Si are elements that improve magnetic properties such as permeability, Fe-Cr-M-based (M is at least one of Al and Si) alloy powder containing at least one of Al or Si in addition to Cr It is preferable as a soft magnetic material powder. Among them, the Fe-Cr-Al-based or Fe-Cr-Al-Si-based alloy powder containing Al as M has superior corrosion resistance compared to the Fe-Si-based or Fe-Si-Cr-based alloy powder, and is easily plastically deformed. That is, by using the Fe-Cr-Al-based or Fe-Cr-Al-Si-based alloy powder, it is possible to obtain a powdered magnetic core having a high point ratio and strength even at a low molding pressure. Therefore, an increase in size and complexity of the molding machine can also be avoided. In addition, since it can be molded at low pressure, damage to the mold is also suppressed and productivity is improved.

In addition, when a metallic soft magnetic material powder such as Fe-Cr-M alloy powder is used as the soft magnetic material powder, an insulating oxide can be formed on the surface of the soft magnetic material powder by heat treatment after molding, as described later. Accordingly, the step of forming the insulating oxide before molding can be omitted, and the method of forming the insulating coating is also simplified, and thus productivity is also improved in this respect.

A case where Fe-Cr-M alloy powder is used as a specific example of the soft magnetic material powder will be described below.

In the Fe-Cr-M series (M is at least one of Al and Si), the base element with the highest content is Fe, followed by Cr and M (Cr and M are in random order). There are many soft magnetic alloy powders. The specific composition of the Fe-Cr-M-based soft magnetic material powder is not particularly limited as long as it can constitute a green magnetic core. Cr is an element that improves corrosion resistance and the like. From this viewpoint, for example, Cr is preferably 1.0% by mass or more. More preferably, Cr is at least 2.5% by mass. On the other hand, Cr is preferably 9.0% by mass or less because the saturation magnetic flux density decreases when it is too large. More preferably, the amount of Cr is 7.0 mass% or less, and still more preferably 4.5 mass% or less.

Like Cr, Al is an element that improves corrosion resistance and the like, and contributes to the formation of surface oxides. In addition, by containing Al as described above, the strength of the green magnetic core is remarkably improved. From this viewpoint, for example, the amount of Al is preferably 2.0% by mass or more. The amount of Al is more preferably 5.0% by mass or more. On the other hand, if Al also becomes too large, the saturation magnetic flux density decreases, and therefore 10.0 mass% or less is preferable. More preferably, it is 8.0 mass% or less, More preferably, it is 6.0 mass% or less. In addition, from the viewpoint of corrosion resistance and the like, the total amount of Cr and Al is preferably 6.0% by mass or more, and more preferably 9.0% by mass or more.

Si has the effect of improving magnetic properties, and can be contained in place of or with Al. In the case of containing Si from the viewpoint of improving the magnetic properties, the amount of Si is preferably 1.0% by mass or more. On the other hand, when the amount of Si is too large, the strength of the green magnetic core decreases, so the amount of Si is preferably 3.0% by mass or less. When strength is prioritized as a required characteristic, it is preferable that Si is an unavoidable impurity level. For example, Si is preferably regulated to less than 0.5% by mass.

The balance other than Cr and M is mainly composed of Fe, but may contain other elements as long as it exhibits advantages such as moldability of the Fe-Cr-M-based soft magnetic material powder. However, since the saturation magnetic flux density and the like of the nonmagnetic element are lowered, it is more preferably 1.0% by mass or less excluding inevitable impurities. It is more preferable that the Fe-Cr-M-based soft magnetic material powder is composed of Fe, Cr, and M, excluding inevitable impurities.

The average particle diameter of the soft magnetic material powder (粒徑; here, the median diameter d50 in the cumulative particle size distribution is used) is not limited thereto, but, for example, one having an average particle diameter of 1 μm or more and 100 μm or less can be used. By reducing the average particle diameter, the strength, core loss, and high-frequency characteristics of the powdered magnetic core are improved. Therefore, the median diameter d50 is more preferably 30 μm or less, further preferably 15 μm or less. On the other hand, when the average particle diameter is small, since the magnetic permeability is lowered, the median diameter d50 is more preferably 5 μm or more.

In addition, the shape of the soft magnetic material powder is not particularly limited. For example, it is preferable to use a granular powder typified by an atomized powder from the viewpoint of fluidity and the like. Atomizing methods, such as gas atomization and water atomization, are suitable for producing powders of alloys which have high malleability and ductility and are difficult to pulverize. Further, the atomizing method is also preferable to obtain a powder of a soft magnetic material having a substantially spherical shape.

Next, the binder used in the first step will be described. When the binder is press-molded, it binds the powders and imparts strength to the molded body to withstand grinding or handling after molding. The type of the binder is not limited thereto, but various types of thermoplastic organic binders such as polyethylene, polyvinyl alcohol (PVA), and acrylic resin may be used. The organic binder is thermally decomposed by heat treatment after molding. Therefore, it is also possible to use together an inorganic binder such as a silicone resin that solidifies and remains to bind the powders even after the heat treatment. However, in the method of manufacturing a powdered magnetic core according to the present invention, since the oxide layer formed in the fourth step has an action of binding soft magnetic material powders, it is preferable to simplify the process by omitting the use of the inorganic binder.

The amount of the binder added may be such that it spreads sufficiently evenly between the soft magnetic material powders and ensures sufficient strength of the molded body. On the other hand, if this is too much, the density and strength will fall. For example, it is preferable to use 0.25 to 3.0 parts by weight per 100 parts by weight of the soft magnetic material powder. In order to withstand the grinding processing performed in the third step, etc., 0.5 to 1.5 parts by weight is more preferable.

The mixing method of the soft magnetic material powder and the binder in the first step is not particularly limited. The mixture obtained by mixing is preferably provided by a granulation process from the viewpoint of moldability and the like. Various methods can also be applied to such a granulation process, but it is particularly preferable that the first process has a spray drying process as the granulation process after mixing the soft magnetic material powder and the binder. In such a spray drying process, a slurry-like mixture containing a soft magnetic material powder and a binder, and a solvent such as water is spray dried using a spray dryer. By spray drying, the particle size distribution is sharp, and granulated powder with a small average particle diameter can be obtained. By using such granulated powder, the workability after molding, which will be described later, is improved. By using a granulated powder having a fine and uniform particle diameter, even if it is cut at the grain boundaries of the granulated powder during grinding or the like, irregularities on the processed surface are small, and chipping and the like are also suppressed. By performing granulation by spray drying, the average (R _AS ) of the arithmetic mean roughness (Ra) of the unprocessed surface (e.g., the outer surface of the flange portion, which is an axial end surface) in the green powder core after heat treatment in the fourth step For example, the ratio (R _MD /R _AS ) of the average (R _MD ) of the arithmetic mean roughness (Ra) of the processed surface (eg, the surface of the conductor wire wound portion) may be 5 or less. More preferably, the ratio (R _MD /R _AS ) is 3 or less. By reducing the unevenness of the processed surface, it is possible to expect a reduction in the risk of damage using the unevenness as a starting point. In addition, as the arithmetic mean roughness, an area of 0.3 mm ² or more per place is evaluated at a plurality of locations using an ultra-depth shape measuring microscope, and the average value is used. Further, by spray drying, a substantially spherical granulated powder is obtained, so that the powder supply property (fluidity of the powder) during molding is also improved. The average particle diameter (median diameter d50) of the granulated powder is preferably 40 to 150 μm, and more preferably 60 to 100 μm.

On the other hand, spray-drying granulation is not essential as an assembling method (FIG. 2). For example, the Fe-Cr-Al-based soft magnetic material powder in which M is Al is particularly excellent in moldability, and thus a molded article having high strength can be provided for grinding or the like. Therefore, chipping and the like in grinding processing and the like are suppressed.

When a method other than spray drying is applied as a granulation method such as electric granulation, for example, in a state in which a binder is mixed, the mixed powder becomes agglomerated powder having a wide particle size distribution due to its binding action. By passing such a mixed powder through a sieve using, for example, a vibrating sieve, it is possible to obtain a granulated powder having a desired secondary particle diameter suitable for molding.

In order to reduce friction between the powder and the mold during pressure molding, it is preferable to add a lubricant such as stearic acid or stearate to the granulated powder. The amount of the lubricant to be added is preferably 0.1 to 2.0 parts by weight based on 100 parts by weight of the soft magnetic material powder. On the other hand, the lubricant may be applied to the mold or sprayed.

Next, a second step of pressing the mixture obtained through the first step will be described. The mixture obtained in the first step is preferably granulated as described above and provided to the second step. The assembled mixture is press-molded into a predetermined shape such as a cylindrical shape, a rectangular parallelepiped shape, and a toroidal shape using a molding mold. The molding in the second step may be room temperature molding, or may be warm molding performed by heating to the extent that the organic binder does not disappear.

In the second step, it is not always necessary to obtain a near net shape molded body. This is because grinding processing or the like is performed in a third step described later.

Next, a third step in which at least one of grinding and cutting is performed on the molded article obtained through the second step will be described. Mechanical processing, such as grinding, is a processing for forming a molded body into a predetermined shape and size. Grinding can be performed using a grinding wheel or the like, and cutting can be performed using a cutting tool. Grinding processing and the like include processing for purposes such as deburring using a brush attached with abrasive particles, and it is preferable to perform at least a wire winding portion of the powder core. This is because the processing step becomes complicated when processing for forming a predetermined shape or the like is performed after the heat treatment described later, such as processing of the wire winding portion. It is more preferable to apply the third step to a metal powder core of a shape having a concave portion that is difficult to process after heat treatment, such as a drum shape having flange portions on both ends of the wire winding portion.

In order to prevent chipping and the like during processing in the third step and to increase the processing precision, it is effective to increase the dot ratio of the molded article provided in the third step. On the other hand, excessively increasing the dot ratio of the molded article is inferior in mass production. It is preferable that it is 78-90%, 79-88% is more preferable, and 81-86% is still more preferable as for the droplet ratio of the molded article provided in the 3rd process. In addition, by using an Fe-Cr-Al-based soft magnetic material powder having excellent moldability, it is also possible to increase the drop ratio of the molded article provided in the third step to 82% or more even at a low molding pressure. In the second step, the dot ratio of the molded article can be adjusted within such a range by adjustment of the molding pressure or the like. In addition, the dot ratio (relative density) of the molded article provided in the third step is calculated by dividing the density of the molded article by the true density of the soft magnetic material powder. In this case, the mass content of the binder or lubricant contained in the molded body is subtracted from the mass of the molded body based on the amount added. Further, the true density of the soft magnetic material powder can be the density of an ingot produced by dissolving in the same composition.

The drum shape has a protruding flange portion at both ends of the column-shaped conductor wire winding portion. For example, the wire winding portion has a cylindrical shape, and the flange portions at both ends thereof are in the shape of a disk, the wire winding portion has a cylindrical shape, the flange on one end thereof has a disk shape and the other end is in a square plate shape, and the conductor winding portion has a cylindrical shape and the The flange portions at both ends may be in the shape of a square plate, the wire winding portion is in the shape of a square column, and the flange portions at both ends thereof are in the shape of a square plate, but the present invention is not limited thereto. When the configuration of the present invention is applied to a flat drum-shaped metal powder core having at least one maximum dimension of the flange portions at both ends larger than the height of the drum shape, that is, the dimension in the axial direction, the effect is remarkable. In addition, such as a shape in which the maximum dimension of the flange portion is two or more times the core diameter (diameter of the wire winding portion), the application to the compacting magnetic core having a narrow concave portion and a deep drum shape is more effective. This is because it is difficult to form such a shape in the case of integral molding or processing such as grinding. The maximum dimension means, for example, a diameter if the flange portion has a disk shape, a long diameter if it has an elliptical plate shape, and a diagonal dimension if it is a square plate shape. Further, a shape having a flange portion only at one end of the wire winding portion can also be applied.

As a method of obtaining the drum shape, for example, in the second step, a cylindrical or prismatic molded body is produced, and a concave portion is formed from the side direction of the cylindrical molded body to the central axis direction by grinding or the like. . Since the molded body in the step through the second step is in a shear layer in which an oxide layer to be described later is formed, which imparts high strength to the powder core, grinding processing or the like is easy, and the processing step is greatly simplified.

Next, a description will be given of a fourth step of heat-treating the molded body that has passed through the third step. In order to form an oxide layer containing an element contained in the soft magnetic material powder on the surface of the metal-based soft magnetic material powder constituting the molded body, a heat treatment is performed on the molded body through the third step. For example, when Fe-Cr-M system (M is at least one of Al and Si) is used as the metallic soft magnetic material powder, the following configuration is obtained. When M is Si, that is, when Al is not actively added, in particular, Cr is concentrated in the oxide layer, and on the surface of the soft magnetic material powder, Fe, Cr, and M (Si An oxide layer having a high ratio of Cr to the sum of) is formed. In addition, in the case of containing Al as M, in particular, Al is concentrated in the oxide layer, and on the surface of the soft magnetic material powder, an oxide layer having a higher ratio of Al to the sum of Fe, Cr and M than the alloy phase inside Is formed. In addition, the effect of obtaining good magnetic properties by mitigating the stress strain introduced by molding or the like can be expected by such heat treatment.

The heat treatment can be performed in an atmosphere in which oxygen is present, such as in an atmosphere, a mixed gas of oxygen and an inert gas. In addition, the heat treatment may be performed in an atmosphere in which water vapor exists, such as in a mixed gas of water vapor and an inert gas. Among them, heat treatment in the air is simple and preferable. In addition, the pressure of the heat treatment atmosphere is not particularly limited, but it is preferably under atmospheric pressure that does not require pressure control.

The soft magnetic material powder is oxidized by the heat treatment, and an oxide layer as described above is formed on the surface. Such an oxide layer constitutes a grain boundary phase for the soft magnetic material, and the insulation and corrosion resistance of the soft magnetic material powder are improved. In addition, since such an oxide layer is formed after forming the molded body, it also contributes to bonding between soft magnetic material powders through the oxide layer.

As described above, in the third step, since grinding or cutting is performed, the alloy phase inside the soft magnetic material powder on the machined surface is exposed. On the other hand, since the portion of the alloy phase exposed by the heat treatment in the fourth step is covered with the oxide layer, insulation of the processed surface is ensured. The heat treatment in the fourth step can serve as a combination of deformation removal during molding, bonding between soft magnetic material powders, and formation of an insulating layer on a processed surface, thereby enabling efficient manufacture of a powdered magnetic core having high strength and high insulation.

The heat treatment in the fourth step may be performed at a temperature at which the oxide layer is formed. By this heat treatment, a powdered magnetic core excellent in strength is obtained. In addition, the heat treatment in the fourth step is preferably performed at a temperature at which the soft magnetic material powder is not significantly sintered. When the soft magnetic material powder is remarkably sintered, the core loss also increases. Specifically, the range of 600 to 900°C is preferable, and the range of 700 to 800°C is more preferable. The holding time is appropriately set depending on the size of the metal powder core, the amount of processing, and the allowable range of variation in characteristics. For example, 0.5 to 3 hours are preferable.

In addition, it is also possible to add other steps before and after each of the first to fourth steps.

For example, when there is a concern about the damage of the metal powder core in the third process, such as in the case of manufacturing a metal powder core having a complex shape or a thin part, the strength of the molded body provided in the third process is compared to the molded state. It is desirable to keep it high. Specifically, as shown in Fig. 9, it is preferable to have a preheating step of heating the molded body to a temperature lower than the heat treatment temperature in the fourth step between the second step and the third step described above. By the heat treatment in the fourth step, an oxide layer containing the elements contained in the soft magnetic material powder is formed on the surface of the soft magnetic material powder, and the strength of the resulting green magnetic core is remarkably increased, at a temperature lower than the heat treatment temperature. Even by heating, the strength of the molded body increases. In terms of the effectiveness of heating, the heating temperature in the preheating step is set higher than room temperature, but if the heating temperature is too high, processing in the third step becomes difficult. Therefore, when performing the preheating, it is performed at a temperature lower than the heat treatment temperature in the fourth step. If the heating temperature is, for example, in the case of Fe-Cr-M (M is at least one of Al and Si), Al, Cr, etc. other than Fe among the elements contained in the soft magnetic material powder are oxidized and concentrated at grain boundaries. Temperature or less is preferable, and 300°C or less is more preferable. If the heating temperature is 300°C or less, it is preferable from the viewpoint that it can be applied to other soft magnetic material powders in addition to the Fe-Cr-M-based soft magnetic material powder. Further, in order to increase the effect of improving the strength by heating, the heating temperature is preferably 100°C or higher. When the holding time of heating is too short, the effect of increasing the strength of the molded body is small, and when it is longer than necessary, the productivity decreases, and therefore, it is preferably 10 minutes or more and 4 hours or less. More preferably, it is 30 minutes or more and 3 hours or less. The atmosphere during preheating is not limited to an oxidizing atmosphere. Since the process becomes simple, the atmosphere is preferably in the air.

By passing through the above preheating step, the strength of the molded article provided in the third step can be made greater than 15 MPa.

In addition, before the first step, a preliminary step of forming an insulating film on the soft magnetic material powder by heat treatment or sol gel method may be added. However, in the method for manufacturing a powdered magnetic core according to the present invention, since an oxide layer can be formed on the surface of the soft magnetic material powder by the fourth process, it is more preferable to simplify the manufacturing process by omitting the preliminary process as described above. . In addition, the oxide layer itself does not undergo plastic deformation well. Therefore, by employing the process of forming the oxide layer after forming, in the pressurization of the second step, particularly, the high formability of the Fe-Cr-Al-based or Fe-Cr-Al-Si-based alloy powder can be effectively utilized. I can.

In addition, there are cases in which the magnetic core obtained through the fourth step has burrs, or in some cases, dimensional adjustment is required. In that case, a fifth step of further performing at least one of grinding and cutting, and a sixth step of heat treating the powdered magnetic core obtained through the fifth step are added to the powdered magnetic core obtained through the fourth step, By the heat treatment in the sixth step, an oxide layer containing an element contained in the soft magnetic material powder may be formed on the surface processed in the fifth step.

In the powdered magnetic core obtained as described above, the powdered magnetic core itself exhibits an excellent effect. In other words, in a drum-shaped metal powder core having a typical complex shape, high strength and insulation properties are realized. The specific configuration is, for example, a powdered magnetic core constructed using a metallic soft magnetic material powder, and has a drum shape having a conductor wire winding portion and flange portions at both ends of the conductor winding portion, and the metallic soft magnetic material powder is It is bonded via an oxide layer containing an element contained in a magnetic material powder, and the surface of the wire wound portion is a processed surface, and is a powdered magnetic core having an oxide layer containing an element contained in the soft magnetic material powder.

"The surface of the wire wound part is a processed surface" means that the wire wound part is formed by machining such as grinding or cutting, and the surface of the wire wound part itself is irrelevant. That is, even when an oxide layer is formed on the surface of the wire winding portion formed by machining, the surface of the wire winding portion is a processed surface. In this case, the arithmetic average roughness of the surface of the wire wound portion becomes larger than the arithmetic average roughness of the outer surface of the flange portion. Further, the fact that the metallic soft magnetic material powder is bonded via an oxide layer containing an element contained in the soft magnetic material powder indicates that the high strength and insulation properties are secured even when the above-described machining is performed. In addition, since an oxide layer containing an element contained in a soft magnetic material powder is also provided on the surface of the wire wound portion, even when the wire wound portion is formed by processing, the insulation of the surface of the wire wound portion is also secured.

In addition, by passing through the above-described processes such as spray drying, the surface has a surface that has been processed and a surface that has not been processed, and the arithmetic mean roughness (Ra) of the surface that has not undergone processing (for example, the axial end surface) average processing, for (R _AS) rough surface (e.g., wire wound surface) ratio (R _MD / R _AS) of the mean (R _MD) of the arithmetic mean roughness (Ra) of 5 or less be obtained powder magnetic core have. More preferably, the ratio (R _MD /R _AS ) is 3 or less.

It is preferable that the average of the maximum diameters of each particle of the soft magnetic material powder is 15 μm or less, and more preferably 8 μm or less in the cross-sectional observation of the powdered magnetic core. Since the soft magnetic material powder constituting the green magnetic core is fine, the high-frequency characteristics are particularly improved. On the other hand, from the viewpoint of suppressing a decrease in permeability, the average of the maximum diameter is more preferably 0.5 μm or more. The average of the maximum diameter can be calculated by grinding the cross section of the metal powder core and observing it under a microscope, reading out the maximum diameter for particles present in the field of view of a certain area, and taking the number average. At this time, it is preferable to take an average of 30 or more particles. The soft magnetic material powder after molding is plastically deformed, but in cross-sectional observation, since most of the particles are exposed at the cross-section of a portion other than the center, the average of the maximum diameters is a value smaller than the median diameter d50 evaluated in the powder state.

Further, as described above, by using Fe-Cr-M-based (M is at least one of Al and Si) as the metal-based soft magnetic material powder, a powdered magnetic core having excellent corrosion resistance can be realized. In addition, in the case of using a Fe-Cr-Al-based or Fe-Cr-Al-Si-based soft magnetic material powder containing Al as M, it is preferable to realize excellent moldability and high dot area ratio and powder core strength. Particularly, when the Fe-Cr-Al-based soft magnetic material powder is used, the dot ratio (relative density) of the green magnetic core can be increased with a low molding pressure, and the strength of the green magnetic core is also improved. It is more preferable to use such an action to make the area ratio of the soft magnetic material powder in the heat-treated green magnetic core within the range of 80 to 92%. The reason why such a range is preferable is that the magnetic properties are improved by increasing the dot ratio, but if an attempt is made to increase the dot ratio excessively, equipment-related and cost-related loads increase. The range of a more preferable drop ratio is 84 to 90%.

The configuration of the above-described metal powder core is preferably a flat drum shape in which at least one diameter or one side of the flange portions on both ends is larger than the axial dimension. This is because it is difficult to realize such a shape only by mold molding.

A coil component is provided using the metal powder core and a coil wound around the metal powder core. The coil may be formed by winding a conductor wire around a metal powder core, or by winding it around a bobbin. The coil component including the metal powder core and the coil is used as a choke, an inductor, a reactor, a transformer, or the like.

In addition, the powdered magnetic core may be manufactured in the form of a compacted magnetic core in which only the soft magnetic material powder mixed with a binder or the like is press-molded as described above, or the soft magnetic material powder and the coil are integrally pressed to form a coil encapsulation structure. It can also be manufactured in the form of a powdered magnetic core.

(Example)

(Evaluation of difference in characteristics according to the difference in constituent elements)

In the following manner, first, the properties of various soft magnetic material powders used in a method of manufacturing a powdered magnetic core were confirmed. As Fe-Cr-Al-based soft magnetic material powder, a spherical atomized powder having an alloy composition (Composition A) of Fe-4.0%Cr-5.0%Al in mass percentage was prepared. The average particle diameter (median diameter d50) measured with a laser diffraction scattering type particle size distribution measuring device (La-920 manufactured by Horiba Corporation) was 18.5 μm.

With respect to 100 parts by weight of the soft magnetic material powder, as a binder, an acrylic resin binder of an emulsion (Polysol AP-604 　 solid content 40% manufactured by Showa Polymer Co., Ltd.) was mixed in a ratio of 2.0 parts by weight. The mixed powder was dried at 120°C for 1 hour, passed through a sieve to obtain granulated powder, and the average particle diameter (d50) was set within the range of 60 to 80 μm. Zinc stearate was added and mixed in a proportion of 0.4 parts by weight with respect to 100 parts by weight of the soft magnetic material powder to the granulated powder to obtain a molding mixture.

The obtained mixture was press-molded at room temperature with a molding pressure of 0.91 GPa using a press machine. The dot ratio evaluated by the molded article was 84.6%. The obtained toroidal shaped body was subjected to heat treatment for 1.0 hour at a heat treatment temperature of 800°C in air to obtain a powdered magnetic core (No 1).

Similarly, the alloy composition (composition B) of Fe-Cr-Si-based soft magnetic material powder with a mass percentage of Fe-4.0%Cr-3.5% Si, and Fe-Si-based soft magnetic material powder with a mass percentage of Fe-3.5% Si Using the alloy composition (composition C), each was mixed and press-molded under the same conditions as in the case of No 1 to obtain a molded body. Heat treatment was performed under conditions of 700°C and 500°C, respectively, to obtain a powdered magnetic core (No 2, 3). In addition, in the case of using the Fe-Si-based soft magnetic material powder, the core loss is deteriorated when heat-treated at a temperature exceeding 500°C, so a heat treatment temperature of 500°C was employed.

The density of the green magnetic core produced by the above process was calculated from its dimensions and mass, and the density of the green magnetic core was divided by the true density of the soft magnetic material powder to calculate the dot ratio (relative density). In addition, a load was applied in the radial direction of the toroidal-shaped compact magnetic core, and the maximum weight P(N) at the time of failure was measured, and the indentation strength sigma r (MPa) was obtained from the following equation.

σr=P(D-d)/(Id ² )

(Here, D: outer diameter of the magnetic core (mm), d: thickness in the radial direction of the magnetic core (mm), and I: height of the magnetic core (mm).)

Further, the windings were wound 15 times on the primary side and the secondary side, respectively, and the core loss Pcv was measured under the conditions of a maximum magnetic flux density of 30 mT and a frequency of 300 kHz with a B-H analyzer SY-8232 manufactured by Iwatsu Measurement Co., Ltd. In addition, the initial permeability μi was measured at a frequency of 100 kHz by winding a conductor wire 30 times around the toroidal-shaped compact magnetic core, and using 4284A manufactured by Hewlett-Packard.

[Table 1]

As shown in Table 1, the powdered magnetic cores of Nos. 1 and 2 using Fe-Cr-M-based soft magnetic material powder as soft magnetic material powder were compared to the powdered magnetic core of No. 3 using Fe-Si-based soft magnetic alloy powder, While exhibiting equivalent or higher magnetic properties, the compression ring strength was increased. That is, according to the configurations according to Nos. 1 and 2, it was possible to provide a metal powder core having high strength by simple pressure molding. In addition, the powdered magnetic core of No. 1 made using Fe-Cr-Al-based soft magnetic material powder is a powdered magnetic core of No. 3 using Fe-Si-based soft magnetic material powder and Fe-Cr-Si-based soft magnetic material powder. Compared with the powdered magnetic core of No 2, the dropping ratio and the magnetic permeability were significantly increased. In addition, the crushing strength of the crushed magnetic core of No 1 exhibited a high value of 100 MPa or more, and also exhibited a value of twice or more compared to the crushing magnetic core of the powder of Fe-Cr-Si-based soft magnetic material of No 2. That is, it was found that the composition using the Fe-Cr-Al-based soft magnetic material powder is very advantageous in obtaining high compression strength. In addition, corrosion resistance was evaluated by a separate salt spray test. As a result, corrosion resistance of the powdered magnetic core of No 3 using Fe-Si-based soft magnetic alloy powder was remarkable, and corrosion resistance was insufficient in a severe corrosive environment. Accordingly, it was found that the powdered magnetic core of No 3 using the Fe-Si-based soft magnetic alloy powder is preferably used for applications where low core loss is required while high corrosion resistance is not required. Among the powdered magnetic cores of Nos 1 and 2 in which corrosion was suppressed, the powdered magnetic core of No 1 exhibited better corrosion resistance even than that of the powdered magnetic core of No 2.

With respect to the green magnetic core of No. 1, the cross-section of the green magnetic core was observed using a scanning electron microscope (SEM/EDX), and at the same time, the distribution of each constituent element was investigated. The results are shown in FIG. 3. (a) is an SEM image, and it can be seen that an image having a black color tone is formed on the surface of the soft magnetic material powder (soft magnetic material particle) 1 having a light gray color tone. The average of the maximum diameter was calculated for 30 or more soft magnetic material particles using an SEM image, and it was 8.8 μm. 3(b) to (e) are mappings showing distributions of O (oxygen), Fe (iron), Al (aluminum), and Cr (chromium), respectively. The brighter the color tone, the more target elements are.

Referring to FIG. 3, it can be seen that the surface of the soft magnetic material powder has a lot of oxygen and oxides are formed, and that the soft magnetic material particles, which are alloys, are bonded through the oxide. Further, on the surface of the soft magnetic material powder, the Fe concentration is lower than in the interior, and the Cr does not exhibit a large concentration distribution. On the other hand, Al has a remarkably high concentration at the grain boundaries of the soft magnetic material powder. From this point of view, an oxide layer containing an element contained in the soft magnetic material powder is formed at the grain boundaries of the soft magnetic material powder, and the oxide layer has a ratio of Al to the sum of Fe, Cr and Al than the internal alloy phase. It was confirmed that it was a high oxide layer. Before the heat treatment, the concentration distribution of each constituent element shown in FIG. 3 was not observed, and it was also found that the oxide layer was formed by heat treatment. In addition, it can be seen that the oxide layers of each grain boundary having a high Al ratio are connected to each other.

Also about the powdered magnetic core of No. 2, the cross-section of the powdered magnetic core was observed using a scanning electron microscope (SEM/EDX), and the distribution of each constituent element was examined at the same time. The results are shown in FIG. 4. (a) is an SEM image, and it can be seen that an image having a black color tone is formed on the surface of the soft magnetic material powder 1 having a light gray color tone. 4B to 4E are mappings showing distributions of O (oxygen), Fe (iron), Cr (chromium), and Si (silicon), respectively.

Referring to FIG. 4, even in the green magnetic core of No 2, it can be seen that the grain boundaries of the soft magnetic material powder have a lot of oxygen and oxides are formed, and the state in which the soft magnetic material powders are bonded through these oxides. have. In addition, the soft magnetic material powder also has a lower concentration of Fe than the inside at the grain boundary, and does not show a large concentration distribution of Si. On the other hand, the concentration of Cr at the surface of the soft magnetic material powder is remarkably high. In this respect, an oxide layer containing the elements contained in the soft magnetic material powder is formed on the surface of the soft magnetic material powder, and the oxide layer has a ratio of Cr to the sum of Fe, Cr and Si than the internal alloy phase. It was confirmed that it was a high oxide layer. Before the heat treatment, the concentration distribution of each constituent element shown in Fig. 4 was not observed, and it was also found that the oxide layer was formed by heat treatment. It can also be seen that the oxide layers of each grain boundary having a high Cr ratio are connected to each other.

The powdered magnetic cores of Fe-Cr-M soft magnetic material powders Nos 1 and 2 both contain Cr, but when M does not contain Al, Cr is concentrated in the grain boundaries of the soft magnetic material powder and contains Al as M. In the case of this, it was found that Al is significantly more concentrated in the grain boundaries than Cr.

Subsequently, a spherical atomized powder having an alloy composition (composition D) of Fe-3.9%Cr-4.9%Al-1.9Si as a mass percentage as a Fe-Cr-M soft magnetic material powder having a different Si amount from the composition A, and A spherical atomized powder having an alloy composition (Composition E) of Fe-3.8%Cr-4.8%Al-2.9Si in terms of mass percentage was prepared, and a powdered magnetic core was produced as follows. The average particle diameter (median diameter d50) measured with a laser diffraction scattering type particle size distribution measuring device (LA-920 manufactured by Horiba Manufacturing Co., Ltd.) was 14.7 μm for the atomized powder of composition D and 11.6 μm for the atomized powder of composition E.

For each of the composition D and the composition E, with respect to 100 parts by weight of the soft magnetic material powder, PVA (PVA-205 manufactured by Kuraray Co., Ltd.; solid content 10%) was mixed in a ratio of 2.5 parts by weight as a binder. After drying the obtained mixture at 120° C. for 1 hour, it was passed through a sieve to obtain granulated powder, and the average particle diameter (d50) was set within the range of 60 to 80 μm. Further, with respect to 100 parts by weight of the granulated powder, 0.4 parts by weight of zinc stearate was added and mixed to obtain a molding mixture. The resulting mixture was press-molded at room temperature with a molding pressure of 0.74 GPa using a press machine to obtain a toroidal shaped body having an inner diameter of 7.8 mm, an outer diameter of 13.5 mm, and a thickness of 4.3 mm. The dot ratio evaluated by the molded article was 80.9% (composition D) and 78.3% (composition E), respectively. The molded article obtained as described above was subjected to heat treatment in the air at a heat treatment temperature of 750° C. for 1.0 hour to obtain a powdered magnetic core (Nos 4 and 5). Table 2 shows the results of evaluating magnetic properties and the like in the same manner as in Nos 1 to 3 above.

[Table 2]

As shown in Table 2, the magnetic properties of the green magnetic cores of Nos 4 and 5 using Fe-Cr-Al-Si-based soft magnetic material powder as the soft magnetic material powder have improved magnetic properties compared to the green magnetic core of No 1 by adding Si. . On the other hand, although the crushing strength slightly lowers than the crushing magnetic core of No 1, it is also understood that a sufficient crushing strength of 100 MPa or more can be obtained even under the condition of lowering the molding pressure. That is, containing Si is disadvantageous in obtaining high compression strength, but it has been confirmed that by simultaneously containing Al, high compression strength can be secured.

In addition, cross-section observation of the powdered magnetic core of Nos. 4 and 5 was performed using a scanning electron microscope (SEM/EDX). Like the powdered magnetic core of No. 1, the grain boundary of the soft magnetic material powder contains a lot of oxygen. , It was confirmed that the oxide was formed, and the soft magnetic material powders were bonded through these oxides (FIGS. 5 and 6). In addition, it was confirmed that the concentration of Fe was lower in the grain boundaries of the soft magnetic material, the concentration of Cr did not show a large concentration distribution, and the concentration of Al at the grain boundaries of the soft magnetic material powder was significantly increased.

As described above, among the metal-based soft magnetic material powders, in particular, in the metal-based soft magnetic material powder using Fe-Cr-M-based (M is at least one of Al and Si) soft magnetic material powder, the molded body is heat treated to The superiority of forming an oxide layer containing an element contained in the soft magnetic material powder on the surface of the magnetic material powder was confirmed.

(Example 1)

Hereinafter, an embodiment of the present invention having the first to fourth steps will be described. Using the soft magnetic material powder having the same composition as No 1 (composition A) and the same composition as No 4 (composition D), a drum-shaped metal powder core was produced as follows (No 6 and No 7 respectively). With respect to 100 parts by weight of the soft magnetic material powder, as a binder, PVA (Poval PVA-205 manufactured by Kuraray Co., Ltd.; solid content 10%) was mixed in a ratio of 2.5 parts by weight (first step). After drying the obtained mixture at 120° C. for 1 hour, it was passed through a sieve to obtain granulated powder, and the average particle diameter (d50) was set within the range of 60 to 80 μm. Further, 0.4 parts by weight of zinc stearate was added to 100 parts by weight of the granulated powder, followed by mixing to obtain a mixture to be subjected to pressure molding. The obtained mixture was press-molded at room temperature with a molding pressure of 0.74 GPa using a press machine to obtain a cylindrical molded body (second step). The dimensions of the obtained molded article were φ10.2×7.5 mm. In addition, the dot ratio evaluated by the molded article was 84.0% for the green core of No 6 and 82.3% for the green core of No 7.

On the outer peripheral side of the cylindrical molded body obtained through the second step, grinding processing was performed using a grinding wheel (third step). The shape of the molded body before processing in the third step is shown in Fig. 7(a), and the shape after processing is shown in Fig. 7(b). In the above grinding process, the cylindrical molded body 5 was cut out from the lateral direction, excluding both ends in the axial direction. The shape of the molded article 6 after the grinding process is a drum shape having the cut-out portion as a wire winding portion 7 and flange portions 8 at both ends thereof. The diameter of the flange portion was 10.2 mm, the height was 7.5 mm, and the diameter of the wire winding portion was 4.8 mm. There was no problem of chipping, and workability was good.

The molded article obtained as described above was subjected to heat treatment in the air at a heat treatment temperature of 750° C. for 1.0 hour (4th step) to obtain a powdered magnetic core.

The resistance of the drum-shaped compact magnetic core obtained as described above was evaluated as follows. Silver paste was applied to the circular surface of one flange portion at intervals of 3 mm to form the electrode 9 (Fig. 8(a)), and the resistance within the flange surface was measured (resistance in the flange surface). In addition, the electrode 10 was formed by applying silver paste at 4 mm intervals on both sides of the wire winding portion with the shaft interposed therebetween (FIG. 8(b)), and the resistance of the shaft portion subjected to the grinding process was measured. (Resistance of wire winding part). For resistance measurement, Table 3 shows the results of evaluation by a two-terminal method with a measurement voltage of 300V using 8340A manufactured by ADC.

[Table 3]

As shown in Table 3, the resistance of the wire wound portion subjected to the grinding process showed a high resistance value at the same level as the in-plane resistance of the flange portion, and it was found that sufficient insulation was secured. An oxide layer containing the elements contained in the soft magnetic material powder is formed on the surface of the soft magnetic material powder with the powdered magnetic cores of Nos 6 and 7, and the oxide layer is in the sum of Fe, Cr and Si than the internal alloy phase. It was an oxide layer with a high ratio of Cr to it. In addition, the same oxide layer was formed on the surface of the wire winding portion. On the other hand, for comparison, an attempt was made to produce a drum shape having the above dimensions by grinding after heat treatment, but the powdered magnetic core after the heat treatment was hard, and thus it could not be processed into a predetermined shape. In addition, it was also confirmed that the processed surface was conductive and insulation properties could not be secured. In addition, it was confirmed that even for the green magnetic cores of Nos. 4 and 5, the toroidal surface was ground after the heat treatment, and the processed surface was conductive and the insulating property could not be secured.

(Example 2)

Using the soft magnetic material powder having the same composition (composition A) as in No 1, a drum-shaped powdered magnetic core was produced as follows. To 100 parts by weight of the soft magnetic material powder, PVA (PVA-205 manufactured by Kuraray Co., Ltd., 10% solid content) was added as a binder in a proportion of 10.0 parts by weight, ion-exchanged water was added as a solvent, and mixed to obtain a slurry. . The slurry concentration is 80% by mass. The slurry was sprayed inside the apparatus with a spray dryer, and the slurry was instantaneously dried with hot air adjusted to 240° C. to recover granular granules (first step). After drying the obtained mixture at 120° C. for 1 hour, it was passed through a sieve to obtain granulated powder, and the average particle diameter (d50) was set within the range of 60 to 80 μm. Further, 0.4 parts by weight of zinc stearate was added to 100 parts by weight of the granulated powder, followed by mixing to obtain a mixture to be subjected to pressure molding. The obtained mixture was press-molded at room temperature with a molding pressure of 0.74 GPa using a press machine to obtain a cylindrical molded body (second step). The dimensions of the obtained molded article were φ10.2×7.5 mm. In addition, the dot ratio evaluated by the molded article was 82.5%.

In the same manner as in Example 1, the outer peripheral side surface of the cylindrical molded body obtained through the second step was subjected to grinding processing using a grinding wheel (3rd step). The diameter of the drum-shaped flange portion was 10.2 mm, the height was 7.5 mm, and the diameter of the wire winding portion was 4.8 mm. There was no problem of chipping, and workability was good. The obtained molded article was subjected to heat treatment in air at a heat treatment temperature of 750°C for 1.0 hour to obtain a green magnetic core. An oxide layer containing the elements contained in the soft magnetic material powder is formed on the surface of the soft magnetic material powder of the resulting green magnetic core, and the oxide layer is the ratio of Cr to the sum of Fe, Cr and Si than the internal alloy phase It was this high oxide layer. Further, a similar oxide layer was formed on the surface of the conductor wire winding portion. The processed surface of the obtained metal powder core was smooth compared to that of Example 1. In addition, the arithmetic average roughness (Ra) of the processed surface (the surface of the wire wound portion) and the arithmetic average roughness (Ra) of the non-processed surface (formed punch surface: axial end surface) using a VK-8500 ultra-depth shape measuring microscope manufactured by KEYENCE Was measured. Measurements are performed at a total of 10 locations for 5 powdered magnetic cores at 2 locations on each side (“central part” for the unprocessed surface (molding punching surface) and “center part in the axial direction” on the machined surface (conductor winding surface)). I did. The evaluation area per one place was 0.32 mm ² . The arithmetic mean roughness Ra of the unprocessed surface (molded punch surface) was in the range of 1.10 to 2.01 μm, and the average was 1.40 μm. That is, the arithmetic mean roughness Ra of the non-processed surface (molded punch surface) was suppressed in the range of 2 μm or less. On the other hand, the arithmetic mean roughness Ra of the processed surface was in the range of 3.17 to 4.99 μm, and the average was 4.11 μm. In other words, the average (R _MD ) of the arithmetic mean roughness (Ra) of the processed surface (the surface of the conductor winding part) is 5 μm or less, and than the average (R _AS ) of the arithmetic mean roughness (Ra) of the unprocessed surface (the axial end surface). However, the ratio (R _MD /R _AS ) was suppressed to about 2.9.

(Example 3)

<Preliminary evaluation of strength>

Using the soft magnetic material powder having the same composition (composition A) as in No 1, a drum-shaped powdered magnetic core was produced as follows. To 100 parts by weight of the soft magnetic material powder, PVA (PVA-205 manufactured by Kuraray Co., Ltd., 10% solid content) was added as a binder in a proportion of 10.0 parts by weight, ion-exchanged water was added as a solvent, and mixed to obtain a slurry. . The slurry concentration is 80% by mass. The slurry was sprayed inside the apparatus with a spray dryer, and the slurry was instantaneously dried with hot air adjusted to 240° C. to recover granular granules (first step). After drying the obtained mixture at 120° C. for 1 hour, it was passed through a sieve to obtain granulated powder, and the average particle diameter (d50) was set within the range of 60 to 80 μm. Further, 0.4 parts by weight of zinc stearate was added and mixed with respect to 100 parts by weight of the granulated powder. The obtained mixed powder was press-molded at room temperature with a molding pressure of 0.74 GPa using a press machine to obtain a cylindrical molded body (second step). The dimensions of the obtained molded body are toroidal with an inner diameter of 7.8 mm, an outer diameter of 13.5 mm, and a thickness of 4.3 mm. The dot ratio of the obtained molded article was 81.3%. After preliminary heating treatment with a holding time of 2 hours at a temperature of 150 to 900°C shown in Table 4, strength was evaluated in the same manner as in the above-described green powder cores of Nos. 1 to 5.

Table 4 and Fig. 10 show the dependence of the strength of the molded body on the preheating temperature. As shown in Fig. 10, the strength of the molded body increased with the increase of the preheat treatment temperature. When the preheating temperature was 100°C or higher, the strength of the molded body exceeding 15 MPa was obtained. In addition, the strength change with respect to the preheating temperature in the temperature range of 300°C or less, which is believed to be mainly due to the hardening of the binder, and the temperature range of 500°C or more in which the oxide that strongly binds the metallic soft magnetic material powders is formed. It can be seen that the gradient of is changed. In consideration of performing the processing, it was found that a temperature range of 300°C or less in which the gradient of the intensity change is small and the absolute value of the intensity is not too large is particularly preferable as the preheat treatment temperature.

[Table 4]

<Evaluation of drum-shaped core>

From the results shown in Fig. 10, the preheating temperature was set to 200°C, and a drum-shaped powdered magnetic core was produced. The raw material powder for which the preliminary evaluation of the strength of the molded body was performed was used. It press-molded at room temperature with a molding pressure of 0.74 GPa using a press machine, and obtained the cylindrical molded object (2nd process). The dimensions of the obtained molded article are φ4×1 mm. The dot ratio of the obtained molded article was 81.5%. After holding at 200°C for 2 hours as a preheating process, grinding processing so that the core diameter (diameter of the wire winding portion) becomes 1.75 mm with a diamond wheel having a blade width of 0.35 mm (third step), A drum-shaped powdered magnetic core was produced. In addition, for comparison, a drum-shaped metal powder core was manufactured by a manufacturing method that does not undergo a preheating process. The heat treatment in the fourth step was performed under the same conditions as in No 6 and the like described above. An oxide layer containing the elements contained in the soft magnetic material powder is formed on the surface of the soft magnetic material powder of the resulting green magnetic core, and the oxide layer is the ratio of Cr to the sum of Fe, Cr and Si than the internal alloy phase It was this high oxide layer. Moreover, the same oxide layer was formed also on the surface of a conductor wire winding part.

The powdered magnetic core produced by a manufacturing method that does not undergo a preheating process has cracks at the boundary between the flange portion and the core portion (wire winding portion), or chipping or defects occurred in the outer periphery of the flange, but the powdered magnetic core was subjected to the preheating process. There were no silver cracks, chipping or defects. In other words, it was possible to achieve high quality without defects even in a drum-shaped metal powder core having a diameter (maximum dimension) of the flange portions on both ends of which is twice the axial dimension or more and having a high flatness.

1 to 4 soft magnetic material powder (soft magnetic material particles)
5 molded body
6 Molded body (after grinding)
7 Conductor winding part
8 Flange part
9 electrodes
10 electrodes

Claims (10)

As a method of manufacturing a powdered magnetic core using a metallic soft magnetic material powder (except ferrite),
A first step of mixing the soft magnetic material powder and the binder,
A second step of press-molding the mixture obtained through the first step, and
A third step of performing at least one of grinding processing and cutting processing on the formed article obtained through the second step to obtain a formed article having a processed surface and a non-processed surface; and
A fourth step of forming an oxide layer containing an element contained in the soft magnetic material powder on the surface of the soft magnetic material powder by heat-treating the molded body having the processed surface and the non-processed surface that has passed through the third step, ,
The ratio of the average (R _MD ) of the arithmetic average roughness (Ra) of the processed surface to the average (R _AS ) of the arithmetic average roughness (Ra) of the unprocessed surface in the powdered magnetic core after heat treatment in the fourth step (R _MD /R _AS ) 5 or less, characterized in that the manufacturing method of the powder magnetic core. The method according to claim 1,
The first step includes a step of spray-drying a slurry containing the soft magnetic material powder and a binder. The method according to claim 1,
The method for producing a powdered magnetic core, wherein the soft magnetic material powder is an Fe-Cr-Al-based soft magnetic material powder. The method according to claim 1,
And a preheating step of heating the molded body to a temperature lower than the heat treatment temperature in the fourth step between the second step and the third step. The method according to claim 1,
The method of manufacturing a powder magnetic core, characterized in that the dot ratio of the molded article provided in the third step is 78 to 90%. The method according to claim 1,
At least one of the grinding processing and the cutting processing is performed at least on a wire winding portion of the powder magnetic core. The method of claim 6,
A method for manufacturing a powdered magnetic core, wherein the shape of the powdered magnetic core is a drum shape having flange portions on both ends of the wire winding portion. As a powdered magnetic core having a processed surface and a non-processed surface made of metallic soft magnetic material powder (except ferrite),
It is a drum shape having a conductor wire winding portion and flange portions at both ends of the conductor winding portion,
The soft magnetic material powder is bonded via an oxide layer containing an element contained in the soft magnetic material powder,
The surface of the wire winding portion is the processed surface, and has an oxide layer containing an element contained in the soft magnetic material powder,
The ratio (R _MD / R _AS ) of the average (R _MD ) of the arithmetic mean roughness (Ra) of the processed surface to the average (R _AS ) of the unprocessed surface arithmetic mean roughness (Ra) is 5 or less. It's made with a crushed heart. The method of claim 8,
In the drum shape, at least one maximum dimension of the flange portions at both ends is larger than the dimension in the axial direction. The method of claim 8,
A powder magnetic core, characterized in that the soft magnetic material powder is an Fe-Cr-Al-based soft magnetic material powder.

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